Fireflies sparkle in wetlands within the Boulder Creek floodplain. Look for them after sunset at Sawhill Ponds, Twin Lakes and in wet meadows west of Cherryvale Road.

Young peregrine falcons fledge from their nests on bare ledges in the Flatirons. Listen for their screams over forests and meadows bordering the Mesa Trail.

Aphrodite and northwestern fritillary butterflies emerge by the thousands in foothills canyons.

Toward the end of the month, south-migrating shorebirds and black-headed Franklin's gulls may congregate on mud flats at Boulder Reservoir and Union Reservoir.

During May and June, clouds of lemon-yellow ponderosa pine pollen swirled up from the mesas west of Boulder.

For weeks, a yellow sheen coated cars and porches throughout Boulder County.

After four years of producing few seeds, most foothills ponderosa pines now sport hundreds of stamen clusters and sprouting cones. As the cones ripen and dry during the next 18 months, their seeds and the insects the cones attract will provide food for squirrels, songbirds and other wildlife.

During our last significant ponderosa pine cone crop in the Boulder Mountain Park five years ago, raucous flocks of red crossbills and pine siskins descended on the forest. These birds, known as irruptive seedeaters, follow cone crops throughout North American conifer forests.

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Crossbills will travel hundreds of miles searching for conifer cone crops, then nest wherever they find them. In January 1995, Allenspark naturalist Nan Lederer found a white-winged crossbill, a Colorado rarity, calmly sitting on her nest in a snow-flocked Engelmann spruce near Brainard Lake, at 10,500 feet.

Clark's nutcrackers, large jays who spend most of their lives in subalpine forests near tree line, may sail down to the foothills to feast on pine seeds. A single nutcracker can store up to 100 seeds in a pouch beneath its tongue, and individuals radiate miles from foraging areas to cache seeds in the ground and under rocks. Recent studies suggest that limber pines growing near the Pawnee Buttes, 50 miles out onto the prairie, were inadvertently planted by Clark's nutcrackers.

Seed-eating birds provide prey for northern pygmy-owls, northern goshawks and other predators. Abert's squirrels also benefit. These graceful black tree-dwellers depend on ponderosa pine seeds and twigs to see them through the winter.

Some ecologists believe that cyclical variation in seed production by conifers serves as a defense against predators. By producing poor seed crops periodically, conifers may control populations of seed-dependent species.

University of Colorado ecologist Carl Bock, who studied conifer seed crops and songbird irruptions in subalpine regions of North America and Asia, concluded that seed crop fluctuations often synchronize over large geographic areas. Amazingly, spruces and firs in northern Siberia and northern Canada tend to produce bumper seed crops during the same years.

Ponderosa pine seed crops appear more erratic, with the amount of cone production often varying from ridge to ridge. But this spring, most of the ponderosas west of Boulder appeared to be producing epic numbers of stamens and cones.

These prolific conifers could be responding to the abundance of moisture in the soil after our September downpours. Or they could be operating under some kind of long-term biological clock that we know nothing about.

Either way, their irruption of sexual activity will have profound effects on local populations of dozens of bird and mammal species.

Ruth Carol Cushman and Stephen Jones are authors of "Wild Boulder County" and "The North American Prairie."

Ponderosa pine stamen clusters produce clouds of golden pollen. Once pollinated, the seed-bearing cones may take more than a year to fully develop and dry. (Stephen Jones/courtesy photo)

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